Apparatus for tomography



March 19, 1963 P. LE G0 APPARATUS FOR TOMOGRAPHY 2 Sheets-Sheet 1 FiledJuly 22, 1955 March 19, 1963 P. LE G6 APPARATUS FOR TOMOGRAPHY 2Sheets-Sheet 2 Filed July 22, 1955 United States Patent 3,082,321APPARATUS FOR TOMOGRAPHY Pierre Le G6, 112 Rue de Maubeuge, Paris,France Filed July 22, 1955, Ser. No. 523,891 Claims priority,application France Aug. 10, 1954 3 Claims. (Cl. 250-615) The presentinvention relates to apparatus for tomography and is more particularlydirected to means for carrying into effect the methods of automatic andhigh-speed tomography of the kind described by the present applicant inhis French patent of the 18th February 1954 for Improvements in Methodsand Devices for Radiography.

An object of the invention is the creation of an apparatus which enablesa series of tomographic sections to be obtained automatically in asshort a time as possible by means of an arrangement of simple andeconomic construction which is easy to use.

The apparatus in accordance with the invention comprises, in the :knownmanner, an oscillating equipment constituted by an X-ray generating unitand a photographic unit arranged respectively at the two extremities ofa telescopic arm pivotally mounted on an axis which defines the plane ofthe section and a mechanism for driving the said oscillating equipmentwith a to-and-fro motion which displaces the two units in oppositedirections along straight line trajectories parallel to the said plane.The apparatus 7 is especially remarkable in that the driving mechanismfor the oscillating system is constituted by a connecting rod and cranksystem, the crank of which is fixed on the shaft of a motor running atconstant speed, the connecting rod being coupled to either of the twounits of the oscillating equipment which are guided by usual means alongtheir straight-line trajectories.

By virtue of this arrangement, a continuous and regular movement of theoscillating system is obtained, following a sinusoidal law of motion, oneither side of a mean position: the passage in one direction or in theother from this mean position is effected at a speed which is determinedby the speed of rotation of the motor, whilst the deceleration, thechange in direction and the acceleration of the movement at the twoextremities of the trajectory of each unit are perfectly progressive.The active periods of emission of the X-ray generator and of exposure ofthe photographic unit correspond to the passages between two positionschosen at equal distances on each side of the mean position, whilst theintermediate periods are utilised for the changing of the image, that isto say the displacement of the film in the photographic unit.

The speed-s of displacement of the X-ray generator unit and thephotographic unit will thus not be constant but will decreaseon eachside of the mean position; calculation and experience have shownhowever, that these variations in speed, with the condition that acertain useful angle is not exceeded, are small in practice and they arenot only not troublesome but on the contrary, by their nature they tendto improve the quality of the images obtained.

The invention also contemplates alternative forms of construction of thedriving mechanism, which alternative forms enable a uniform speed ofdisplacement of the X-ray generator unit and the photographic unit to beobtained in case of need, or which may result in other more favourableeventual laws of movement, for example motions of constant accelerationor deceleration.

In accordance with one preferred form of embodiment, the axis ofoscillation, and in consequence the position of the plane of section, isheld fixed in space, the displace ment of section with respect to thesubject being effected by movement of the said subject; this movementmay be chosen with advantage to be continuous, since the for- 3,682,321Patented Mar. 19, 1963 ward movement carried out during the period of anexpo sure remains of the order of the thickness of section.

On the other hand, the invention also contemplates an extension of theapparatus described to tomoscopy, in such manner as to permit of the useof the high speed of exploration obtained for the production of animmediate view of the image of the section moving in depth from one sideto the other of the subject under examination.

The special features and advantages of the invention will furthermore bebrought out in the course of the description which follows below of oneexample of embodiment, reference-being made to the attached diagrammaticdrawings in which:

FIG. 1 is a view in elevation of an apparatus in accordance with theinvention.

FIG. 2 is a detail view relative to an alternative form of constructionof the driving mechanism.

FIG. 3 shows in diagrammatic form, a method of embodiment of atomoscopic system.

FIG. 4 is a similar View relative to a further form of tomoscopicdevice.

In accordance with the form of embodiment chosen and shown in FIG. 1,the apparatus comprises an X-ray generator unit 1 and a photographicunit 2 mounted on the two extremities of a telescopic arm 3 pivoted on afixed axis 4. Since the units 1 and 2 are guided by any known means soas to follow the trajectories XX and Y-Y, which are vertical in thepresent case, the plane of tomographic section is the plane Z-Z whichcontains the axis 4.

The subject to be examined is placed on a support 5 in the form of atrolley to which can be imparted a continuous movement at right-anglesto the plane of section Z-Z, for example by means of a screw 6 coupledto a motor 7 and engaged in a threaded sleeve 8 rigidly fixed to thesaid trolley. This movement may be made non-continuous if it is sodesired, for example by adding a mechanical or electro-magnetic clutchbetween the screw 6 and the motor '7, the clutch being controlled by theelectrical device which ensures the completion of exposure of onenegative and the beginning of the next following.

The photographic unit 2 is coupled by means of a connecting rod 10 to acrank 11 which is itself keyed on the shaft of a motor 12 of theconstant speed type, the speed being adjustable. Along the circle shownin chain-dotted lines, which corresponds to the trajectory of the crankpin, there will be in succession an active rising period AB (therotation being supposed to be in the direction of the hands of a watch),an intermediate period BC, an active falling period CD, and a secondintermediate period DA. The active periods extend over an angle ofrotation a on each side of the mean position at which the arm 3 and thecrank 11 are horizontal. If t is the duration of an active period, t isthat of an intermediate period and T is the duration of one revolutionof the motor; taking for example a=45, then t=t'=T/4. If the motor isrotating for example at 300 revolutions per minute, then T=0.2 sec- 0nd,and r=z=50 milli-seconds.

The linear speed of the X-ray generator and the photographic unit duringthe period of emission of X-rays varies, in these conditions by about29% between the mean position and the points A, B, for example, from thebeginning and from the end of the active travel. The influence of thisvariation in speed on the quality of the tomographic negative issubstantially nil, since the extreme positions and thus the lowestspeeds correspond to the greatest differences between the source ofX-ray emission and the sensitive surface of the photographic unit,whilst at the central position at which the speed is a maximum, thiscorresponds to the minimum distance between the source of X-rays and thesensitive surface of the photographic plate. The X-ray energy receivedper unit of time by this plate is thus greater at this moment than atthe extreme positions, but as the displacement is faster, the energyreceived as a function of the linear displacement remains substantiallyconstant.

One method of operation consists in applying the hightension to theX-ray generator unit during each of the rising or falling activeperiods, and in causing the film to be changed in the photographic unitduring each of the intermediate periods; this enables the maximum rateof operation to be obtained and gives, in the case of the numericalexample cited, section images per second. As the speed of movement ofthe subject is regulated to one centimetre per second, there will beobtained under these conditions a succession of 60 section images in 6seconds, the images being spaced apart by one millimetre.

It is, of course, also possible to apply the high-tension to the X-rayunit, not during each active period but only once for every 2: periods,and this, if the other conditions remain the same as those indicatedabove, will give a space between successive sections of 2, 3, 4 nmillimetres, whilst maintaining the same thickness of section and thesame time of exposure of 50 milli-seconds for each tomograph.

The control of the high-tension circuit of the X-ray unit 1 on the onehand, and of the winding mechanism for the film in the photographic uniton the other hand, in dependence on the movement of the crank and rodsystem, or more generally of the movement of the oscillating equipment,does not lead to any difficulty at all and thus will require no furtherdescription.

In the foregoing description also, no details have been given of theconstruction of the photographic unit, which has no direct bearing onthe real object of the invention; it is however clear that photographicunits provided with an intensity amplifier find an especially usefulapplication in this case by reason of their qualities of lightness andsensitivity which enable the inertia of the oscillating equipment to beconsiderably reduced, and in consequence the speed of operation may besubstantially increased. The photographic apparatus may then beconstituted by a camera of the cinema type or by a more simplephotographic apparatus using films of any desired size (7 x 7 cm. forexample) with the proviso that the film can be wound forward betweeneach exposure.

On the other hand, the invention is in no way limited to the use of arod and crank system per se, and any other similar mechanism adapted toconvert a circular movement to a reciprocating motion may be substitutedtherefor. Thus, in order to obtain a constant speed of move ment, forexample during the active period of each cycle, recourse may be had tothe alternative form of mechanism shown in FIG. 2, in which thecrank-pin 14, forming the pivotal mounting of the crank-arm 10 on thedriving crank 11, is arranged to slide in a slot provided in the crankinstead of being fixed to the said crank. The crank-pin is urged by acompression spring against a cam 16 fixed with respect to the drivingshaft 17. The profile of this cam Will be designed in such manner forexample, that the speed of displacement of the X-ray unit and thephotographic unit is constant during the active period and the rates ofacceleration and deceleration are constant during the inactive periodsof each cycle, corresponding to the reversals in direction of themovement and to the forward movement of the film.

The tomographic equipment in accordance with the invention and asdescribed above, has important practical advantages as compared withpreviously known types of tomographic equipment, and especially in thatit permits of a very rapid sequence of images to be obtained, the speedof which is such that the definition of the successive images issubstantially unaifected by any movement of the subject or patient, suchas for example when breathing during examination of the lungs, thusenabling a valid comparison to be obtained between the successive imagesforming the sequence of the corresponding sections.

FIG. 3 shows a form of embodiment of a tomoscope in accordance with theinvention. The optical unit 2' comprises an intensity amplifier, and thephotographic device provided (a simple photographic apparatus or acamera of the cinematograph type) is removed from the unit and isreplaced by a telescopic dark chamber (of the bellows type or withtelescopic tubes), which couples the moulded optical unit 2 to a fixedviewing chamber 21. The image (which is supposed in this case to beformed by parallel rays) produced in the unit 2', is transferred throughtwo total-reflection prisms or mirrors 22, 23, to a small monocular orbinocular observation microscope 24, the position of which is fixed inspace, for example by rigid coupling to the fixed frame of theapparatus.

The arrangement shown in FIG. 4 permits of the transmission of imagesformed by beams of divergent or convergent rays, by virtue of the factthat the length of the optical path between the unit 2' and the fixedviewing chamber 21 is maintained constant in spite of the movehand tothe unit 2' and, on the other hand, to the viewing chamber 21, theslider being constantly urged towards the base by a control spring 30.The image produced by the intensity-amplifier unit 2' is transmitted bythe totalrefiection prisms or mirrors 31, 32, 33 and 34, and it is easyto see that the length of the optical path followed remains constant inthe present case, whatever the movements of the unit 2 may be, thesemovements being followed by the dark chamber at half their amplitudes.The dark chamber is in this case coupled on the one hand to the unit 2and to the viewing chamber 21 on the other hand, by two bellows members35, 36, or by suitable corresponding telescopic tubes.

In addition to the advantages of the apparatus of the present inventionin automatic tomography, as already referred to, the very rapid sequenceof images obtained also makes possible the use of automatic tomoscopy,the sequence being adapted to create a clear, static visual image, dueto persistence of vision, as in the technique of cinematography. By thismeans, it becomes possible to observe visually the various tomographicsections of the subject under examination, as the subject is moved atright-angles across the plane comprising the real or virtual axis ofoscillation, such as the axis 4 of FIG. 1.

What I claim is:

1. An apparatus for automatic tomoscopy comprising: an X-ray generatingunit; an optical receiver including a fixed viewing chamber and amovable optical unit, a lightproof dark chamber coupled between saidfixed chamber and said movable unit, an optical system oftotal-refiection devices for transferring the image from said movableoptical unit to said fixed viewing chamber; means for guiding said X-rayunit and said movable optical unit along laterally spaced straightguides; means for continuously oscillating the two said units inopposite parallel directions along said guides at such a high speed thata static visual image, due to persistence of vision, is obtained in saidfixed viewing chamber when the X-ray unit is operated during a fractionof its travel in either direction; and means for impressing movements onsaid optical system of total-reflection devices which are similar to themovements effected to said movable optical unit but of half theirrespective amplitudes, whereby the total length of the optical pathbetween said movable optical unit and said fixed viewing chamber remainsconstant,

notwithstanding the displacements impressed on said movable opticalunit.

2. An apparatus as claimed in claim 1, and further comprising supportingmeans for the subject under examination, and means for continuouslydisplacing said supporting means during the tomoscopic examination, thedirection of the displacement being perpendicular to the direction ofmotion of the said units.

3. An apparatus :as claimed in claim 1, in which the total-reflectionoptical system forms an optical path of invariable length between saidmovable optical unit and said fixed viewing chamber, said optical systembeing contained in the dark chamber and carried by a sliding memberadapted to move with substantially no play along slide-tracks parallelto the direction of movement of said movable unit, said sliding memberbeing suspended from a cable, the extremities of which are respectivelyfixed to said movable unit and said fixed viewing chamber, said cablepassing round a pulley rigidly fixed to the said sliding member, thelatter being urged in a direction opposite to that of the movement ofsaid movable unit by means of a control spring.

References (Zited in the file of this patent UNITED STATES PATENTS2,000,497 Pohl May 7, 1935 2,110,954 Grossmann Mar. 15, 1938 2,353,145Chamberlain July 11, 1944 2,490,400 Berggren Dec. 6, 1949 2,491,224Stava Dec. 13, 1949 2,522,280 Kollmorgen Sept. 12, 1950 2,812,687 Ei'telet al Nov. 12, 1957 FOREIGN PATENTS 910,716 Germany May 6, 1954

1. AN APPARATUS FOR AUTOMATIC TOMOSCOPY COMPRISING: AN X-RAY GENERATINGUNIT; AN OPTICAL RECEIVER INCLUDING A FIXED VIEWING CHAMBER AND AMOVABLE OPTICAL UNIT, A LIGHTPROOF DARK CHAMBER COUPLED BETWEEN SAIDFIXED CHAMBER AND SAID MOVABLE UNIT, AN OPTICAL SYSTEM OFTOTAL-REFLECTION DEVICES FOR TRANSFERRING THE IMAGE FROM SAID MOVABLEOPTICAL UNIT TO SAID FIXED VIEWING CHAMBER; MEANS FOR GUIDING SAID X-RAYUNIT AND SAID MOVABLE OPTICAL UNIT ALONG LATERALLY SPACED STRAIGHTGUIDES; MEANS FOR CONTINUOUSLY OSCILLATING THE TWO SAID UNITS INOPPOSITE PARALLEL DIRECTIONS ALONG SAID GUIDES AT SUCH A HIGH SPEED THATA STATIC VISUAL IMAGE, DUE TO PERSISTENCE OF VISION, IS OBTAINED IN SAIDFIXED VIEWING CHAMBER WHEN THE X-RAY UNIT IS OPERATED DURING A FRACTIONOF ITS TRAVEL IN EITHER DIRECTION; AND MEANS FOR IMPRESSING MOVEMENTS ONSAID OPTICAL SYSTEM OF TOTAL-REFLECTION DEVICES WHICH ARE SIMILAR TO THEMOVEMENTS EFFECTED TO SAID MOVABLE OPTICAL UNIT BUT OF HALF THEIRRESPECTIVE AMPLITUDES, WHEREBY THE TOTAL LENGTH OF THE OPTICAL PATHBETWEEN SAID MOVABLE OPTICAL UNIT AND SAID FIXED VIEWING CHAMBER REMAINSCONSTANT, NOTWITHSTANDING THE DISPLACEMENTS IMPRESSED ON SAID MOVABLEOPTICAL UNIT.